Abstract: Rotary engine construction wherein a lobed rotor cooperates with unique retractable separators to divide the bore into work chambers, the rotor lobes or pistons performing the intake, compression, power and exhaust functions rapidly, efficiently and smoothly, and wherein the simplicity of construction allows the number of firings per rotor revolution, their sequence and the compression ratio to be readily selected for a particular end use. The engine further embodies novel intake and exhaust valves and actuating structure therefor, work chamber inactivation mechanism, and positive oil pumping means.